U.S. patent application number 12/826897 was filed with the patent office on 2012-01-05 for adjustable tuning of a dielectrically loaded loop antenna.
This patent application is currently assigned to Vivant Medical, Inc.. Invention is credited to Kenlyn S. Bonn, Tao Nguyen, Mani N. Prakash, Brian Shiu.
Application Number | 20120004650 12/826897 |
Document ID | / |
Family ID | 45400263 |
Filed Date | 2012-01-05 |
United States Patent
Application |
20120004650 |
Kind Code |
A1 |
Shiu; Brian ; et
al. |
January 5, 2012 |
Adjustable Tuning of a Dielectrically Loaded Loop Antenna
Abstract
A microwave antenna assembly is disclosed. The antenna assembly
includes an elongated member defining a longitudinal axis and
having proximal and distal ends. The antenna assembly also includes
an outer conductor and an inner conductor each disposed within the
elongated member and extending along the longitudinal axis. A
portion of the inner conductor is deployable relative to the outer
conductor such that the antenna assembly may transition from a
first configuration to a second configuration. The antenna assembly
also includes an expandable sheath at least partially disposed
about a distal portion of the inner conductor and defining at one
or more lumens configured to couple to a supply of dielectric
material used to regulate the expansion of the expandable
sheath.
Inventors: |
Shiu; Brian; (Sunnyvale,
CA) ; Bonn; Kenlyn S.; (Boulder, CO) ;
Prakash; Mani N.; (Boulder, CO) ; Nguyen; Tao;
(Redwood City, CA) |
Assignee: |
Vivant Medical, Inc.
|
Family ID: |
45400263 |
Appl. No.: |
12/826897 |
Filed: |
June 30, 2010 |
Current U.S.
Class: |
606/33 ;
343/790 |
Current CPC
Class: |
H01Q 9/04 20130101; A61B
2018/1838 20130101; H01Q 1/44 20130101; A61B 2018/1861 20130101;
H01Q 9/0485 20130101; A61B 18/1815 20130101; H01Q 9/16
20130101 |
Class at
Publication: |
606/33 ;
343/790 |
International
Class: |
A61B 18/18 20060101
A61B018/18; H01Q 9/04 20060101 H01Q009/04 |
Claims
1. A microwave antenna assembly comprising: an elongated member
defining a longitudinal axis and having proximal and distal ends;
an outer conductor and an inner conductor each disposed within the
elongated member and extending along the longitudinal axis, at
least a portion of the inner conductor being deployable relative to
the outer conductor such that the antenna assembly may transition
from a first configuration to a second configuration; and an
expandable sheath at least partially disposed about a distal
portion of the inner conductor and defining at least one lumen
configured to couple to a supply of dielectric material used to
selectively expand the sheath.
2. The microwave antenna assembly according to claim 1, wherein the
distal portion of the inner conductor is configured to extend
laterally relative a longitudinal axis of the outer conductor to
define an arcuate profile.
3. The microwave antenna assembly according to claim 2, wherein the
arcuate profile defines an ablation region that at least partially
surrounds an area of tissue to be treated in such a manner that at
least a portion of the area of tissue to be treated is located
within the ablation region.
4. The microwave antenna assembly according to claim 3, wherein the
distal portion of the inner conductor is disposed in contact with
the expandable sheath and the at least one lumen defines a gap
oriented toward the ablation region.
5. The microwave antenna assembly according to claim 3, wherein the
inner conductor has at least one of a substantially hemi-spherical
cross-section and a substantially U-shaped cross-section.
6. The microwave antenna assembly according to claim 3, further
comprising a dielectric permeable core disposed within the at least
one lumen, the core coupled to the inner conductor and an inner
surface of the expandable sheath.
7. The microwave antenna assembly according to claim 1, wherein the
dielectric material is selected from the group consisting of water,
saline, chlorodifluoromethane, nitrogen, nitrous oxide, carbon
dioxide, and mixtures thereof.
8. A microwave ablation system, comprising: an antenna assembly
including: an elongated member defining a longitudinal axis and
having proximal and distal ends; an outer conductor and an inner
conductor each disposed within the elongated member and extending
along the longitudinal axis, at least a portion of the inner
conductor being deployable relative to the outer conductor such
that the antenna assembly may transition from a first configuration
to a second configuration; and an expandable sheath at least
partially disposed about a distal portion of the inner conductor
and defining at least one lumen configured to receive a dielectric
material; and a fill source coupled to the at least one lumen and
configured to regulate the amount of the dielectric material within
the lumen to control the expansion of the expandable sheath.
9. The microwave ablation system according to claim 8, wherein the
distal portion of the inner conductor is configured to extend
laterally relative a longitudinal axis of the outer conductor to
define an arcuate profile.
10. The microwave ablation system according to claim 9, wherein the
arcuate profile defines an ablation region that at least partially
surrounds an area of tissue to be treated in such a manner that at
least a portion of the area of tissue to be treated is located
within the ablation region.
11. The microwave ablation system according to claim 10, wherein
the distal portion of the inner conductor is disposed in contact
with the expandable sheath and the at least one lumen defines a gap
oriented toward the ablation region.
12. The microwave ablation system according to claim 10, wherein
the inner conductor has at least one of a substantially
hemi-spherical cross-section and a substantially U-shaped
cross-section.
13. The microwave ablation system according to claim 10, further
comprising a dielectric permeable core disposed within the at least
one lumen, the core coupled to the inner conductor and an inner
surface of the expandable sheath.
14. The microwave ablation system according to claim 8, wherein the
dielectric material is selected from the group consisting of water,
saline, chlorodifluoromethane, nitrogen, nitrous oxide, carbon
dioxide, and mixtures thereof.
15. A method for performing microwave ablation, the method
comprising the steps of: inserting an antenna assembly into a
tissue volume, the antenna assembly including an outer conductor,
an inner conductor and an expandable sheath at least partially
disposed about a distal portion of the inner conductor and defining
at least one lumen configured to receive a dielectric material;
deploying at least a portion of the inner conductor from the outer
conductor such that the antenna assembly may transition from a
first configuration to a second configuration; regulating an amount
of a dielectric material supplied to the at least one lumen to
control expansion of the expandable sheath; energizing the antenna
assembly to ablate the tissue volume; and withdrawing the
dielectric material from the at least one lumen to deflate the
expandable sheath.
16. The method according to claim 15, wherein deploying step
further includes the step of extending the distal portion of the
inner conductor laterally relative to a longitudinal axis of the
outer conductor to define an arcuate profile.
17. The method according to claim 16, wherein deploying step
further includes the step of defining an ablation region that at
least partially surrounds an area of the tissue volume to be
treated in such a manner that at least a portion of the area of
tissue volume to be treated is located within the ablation
region.
18. The method according to claim 15, wherein the distal portion of
the inner conductor is disposed in contact with the expandable
sheath and the at least one lumen defines a gap oriented toward the
ablation region.
19. The method according to claim 15, wherein the antenna assembly
includes a dielectric permeable core disposed within the at least
one lumen, the core coupled to the inner conductor and an inner
surface of the expandable sheath.
Description
BACKGROUND
[0001] 1. Technical Field
[0002] The present disclosure relates generally to microwave
antennas. More particularly, the present disclosure is directed to
flexible loop antenna having a variable dielectric loading.
[0003] 2. Background of Related Art
[0004] Treatment of certain diseases requires destruction of
malignant tissue growths (e.g., tumors). It is known that tumor
cells denature at elevated temperatures that are slightly lower
than temperatures injurious to surrounding healthy cells.
Therefore, known treatment methods, such as hyperthermia therapy,
heat tumor cells to temperatures above 41.degree. C., while
maintaining adjacent healthy cells at lower temperatures to avoid
irreversible cell damage. Such methods involve applying
electromagnetic radiation to heat tissue and include ablation and
coagulation of tissue. In particular, microwave energy is used to
coagulate and/or ablate tissue to denature or kill the cancerous
cells.
[0005] Microwave energy is applied via microwave ablation antennas
that penetrate tissue to reach tumors. There are several types of
microwave antennas, such as monopole and dipole, in which microwave
energy radiates perpendicularly from the axis of the conductor. A
monopole antenna includes a single, elongated microwave conductor
whereas a dipole antenna includes two conductors. In a dipole
antenna, the conductors may be in a coaxial configuration including
an inner conductor and an outer conductor separated by a dielectric
portion. More specifically, dipole microwave antennas may have a
long, thin inner conductor that extends along a longitudinal axis
of the antenna and is surrounded by an outer conductor. In certain
variations, a portion or portions of the outer conductor may be
selectively removed to provide more effective outward radiation of
energy. This type of microwave antenna construction is typically
referred to as a "leaky waveguide" or "leaky coaxial" antenna.
SUMMARY
[0006] According to one embodiment of the present disclosure, a
microwave antenna assembly is disclosed. The antenna assembly
includes an elongated member defining a longitudinal axis and
having proximal and distal ends. The antenna assembly also includes
an outer conductor and an inner conductor each disposed within the
elongated member and extending along the longitudinal axis. A
portion of the inner conductor is deployable relative to the outer
conductor such that the antenna assembly may transition from a
first configuration to a second configuration. The antenna assembly
also includes an expandable sheath at least partially disposed
about a distal portion of the inner conductor and defining at least
one lumen configured to couple to a supply of dielectric material
used to selectively expand the sheath.
[0007] According to another embodiment of the present disclosure, a
microwave ablation system is disclosed. The system includes an
antenna assembly having an elongated member defining a longitudinal
axis and having proximal and distal ends. The antenna assembly also
includes an outer conductor and an inner conductor each disposed
within the elongated member and extending along the longitudinal
axis. A portion of the inner conductor is deployable relative to
the outer conductor such that the antenna assembly may transition
from a first configuration to a second configuration. The antenna
assembly also includes an expandable sheath at least partially
disposed about a distal portion of the inner conductor and defining
at least one lumen configured to receive a dielectric material. The
system includes a fill source coupled to the lumen and configured
to regulate the amount of the dielectric material within the lumen
to control the expansion of the expandable sheath.
[0008] A method for performing microwave ablation is also
contemplated by the present disclosure. The method includes the
initial step of inserting an antenna assembly into a tissue volume.
The antenna assembly includes an outer conductor, an inner
conductor and an expandable sheath at least partially disposed
about a distal portion of the inner conductor and defining at least
one lumen. The method also includes the steps of deploying at least
a portion of the inner conductor from the outer conductor such that
the antenna assembly may transition from a first configuration to a
second configuration and regulating an amount of a dielectric
material supplied to the at least one lumen to control expansion of
the expandable sheath. The method further includes the steps of
energizing the antenna assembly to ablate the tissue volume and
withdrawing the dielectric material from the at least one lumen to
deflate the expandable sheath.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] The above and other aspects, features, and advantages of the
present disclosure will become more apparent in light of the
following detailed description when taken in conjunction with the
accompanying drawings in which:
[0010] FIG. 1 is a perspective view of a microwave ablation system
according to an embodiment of the present disclosure;
[0011] FIGS. 2A-2B are cross-sectional views of a feedline
according to an embodiment of the present disclosure;
[0012] FIG. 3 is a partial, cross-sectional view of a microwave
antenna assembly according to an embodiment of the present
disclosure;
[0013] FIG. 4 is a partial, cross-sectional view of the microwave
antenna assembly of FIG. 2 in a partially deployed configuration
according to an embodiment of the present disclosure;
[0014] FIG. 5 is a top view of the microwave antenna assembly of
FIG. 2 in a fully deployed configuration according to an embodiment
of the present disclosure;
[0015] FIG. 6 is a cross-sectional view of the microwave antenna
assembly of FIG. 5 according to an embodiment of the present
disclosure;
[0016] FIG. 7 is a cross-sectional view of another embodiment of a
microwave antenna assembly according to an embodiment of the
present disclosure;
[0017] FIG. 8 is a cross-sectional view of another embodiment of a
microwave antenna assembly according to an embodiment of the
present disclosure;
[0018] FIG. 9 is a cross-sectional view of another embodiment of a
microwave antenna assembly according to an embodiment of the
present disclosure;
[0019] FIG. 10 is a top view of a microwave antenna assembly in a
fully deployed configuration according to an embodiment of the
present disclosure;
[0020] FIG. 11 is a cross-sectional view of the microwave antenna
assembly of FIG. 10 in a deflated configuration according to an
embodiment of the present disclosure;
[0021] FIG. 12 is a cross-sectional view of the microwave antenna
assembly of FIG. 10 in an inflated configuration according to an
embodiment of the present disclosure;
[0022] FIG. 13 is a cross-sectional view of another embodiment of a
microwave antenna assembly in a deflated configuration according to
an embodiment of the present disclosure;
[0023] FIG. 14 is a cross-sectional view of the microwave antenna
assembly of FIG. 13 in an inflated configuration according to an
embodiment of the present disclosure; and
[0024] FIG. 15 is a flow chart of a method according to an
embodiment of the present disclosure.
DETAILED DESCRIPTION
[0025] Particular embodiments of the present disclosure are
described herein below with reference to the accompanying drawings.
In the following description, well-known functions or constructions
are not described in detail to avoid obscuring the present
disclosure in unnecessary detail. In the drawings and in the
description that follows, the term "proximal," as is traditional,
will refer to the end of the apparatus that is closest to the
clinician, while the term "distal" will refer to the end that is
furthest from the clinician.
[0026] Referring to FIG. 1, a microwave tissue treatment system 10
in accordance with an embodiment of the present disclosure is
shown. System 10 includes a microwave antenna assembly 100
connected to a power source or supply 20, e.g., a microwave or RF
generator or any suitable power generating device suitable for
energizing the antenna assembly 100, through a feedline 30. The
power supply 20 is configured to provide microwave energy at an
operational frequency from about 300 MHz to about 10,000 MHz.
[0027] The system 10 also includes a fill source 40, e.g., an
electric motor pump, a peristaltic pump or the like, as a mechanism
for circulating a dielectric material "M," such as gas (e.g.,
nitrogen, air, etc.) or liquid (e.g., saline, water, etc.) through
the antenna assembly 100, as described below. Antenna assembly 100
may further include a pusher or deployment assembly 50 that
includes a deployment knob 52 operatively engaged with or coupled
to the antenna assembly 100, as described in further detail
below.
[0028] Referring now to FIGS. 1-2B, as indicated above, antenna
assembly 100 is electrically connected to generator or power supply
20 by feedline 30. Feedline 30 may be any suitable conductive
pathway capable of transferring an electrical current to antenna
assembly 100. In one embodiment, as seen in FIGS. 2A-2B, feedline
30 may be a coaxial cable composed of an inner conductor 102, an
outer conductor 104, and an inner insulator 106 interposed between
inner and outer conductors 102, 104 to electrically separate and/or
isolate inner and outer conductors 102,104 from one another. Inner
and outer conductors 102, 104 may each be made of a suitable
conductive material that may be semi-rigid or flexible, while inner
insulator 106 may include any number of suitable non-conductive
materials such as ceramic and polytetrafluoroethylene (PTFE). Inner
and outer conductors 102, 104 of feedline 30 may incorporate any
suitable conductive material or metal, including, but not limited
to, silver, copper and gold. In certain embodiments, inner and
outer conductors 102, 104 of feedline 30 may include a conductive
or non-conductive substrate plated or coated with a suitable
conductive material. The inner conductor and outer conductor 104
may be constructed of copper, gold, stainless steel or other
conductive metals with similar conductivity values.
[0029] Feedline 30 may range in length from about 1 foot (0.3048 m)
to about 15 feet (4.572 m), or greater depending on a particular
application. In one embodiment, the feedline 30 may be formed from
a coaxial, semi-rigid or flexible cable having a wire with a
0.047'' outer diameter rated for 50 Ohms. As depicted in FIG. 1,
feedline 30 has a proximal portion 108 operatively connected to, or
connectable to, power supply 20 at proximal end 110, and a distal
portion 112 that forms a part of microwave antenna assembly 100, as
disclosed below. In some embodiments, the feedline 30 and power
supply 20 may be a part of an integrated handheld device.
[0030] Referring now to FIGS. 1, 3-5, the antenna assembly 100
includes an elongated member 114 disposed about the distal portion
112 of feedline 30, and a sheath 116 that at least partially
surrounds a distal portion 102a (FIG. 3) of the inner conductor
102, as described in further detail below. Elongated member 114 has
proximal and distal ends 118, 120 and defines longitudinal axis
"A." Elongated member 114 may be formed of any material suitable
for electrically insulating a clinician or operator from the inner
and outer conductors 102, 104 of feedline 30 disposed therein such
that the antenna assembly 100 may be handled during use.
[0031] In non-deployed configuration, the elongated member 114
conceals a distal portion 102a (FIG. 3) of the inner conductor 102
when the microwave antenna assembly 100 is not in use so as to
prevent unintentional damage or injury. In particular, the
elongated member 114 conceals the distal portion 112 of feedline
30, which includes distal portions 102a, 104a, and 106a of the
inner conductor 102, the outer conductor 104, and the inner
insulator 106, respectively. Accordingly, the inner conductor 102,
the outer conductor 104, and the inner insulator 106 also
constitute components of antenna assembly 100.
[0032] At least a portion of the inner conductor 102, i.e. distal
portion 102a, is deployable relative to distal portion 104a of the
outer conductor, such that the antenna assembly 100 may transition
from a first, non-deployed configuration (FIG. 3), to a second,
deployed configuration during use (FIGS. 4 and 5), as described in
further detail below. In the first condition, the distal portion
102a of the inner conductor is at least partially disposed within
the distal portion 104a of the outer conductor and the elongated
member 114. In the second, deployed configuration, the distal
portion 102a of the inner conductor extends at least partially
beyond a distal end 120 of elongated member 114, such that contact
may be made with the target tissue.
[0033] Movement from the first configuration to the second
configuration may be facilitated through the use of any suitable
mechanism, such as, for example, a deployment assembly 50 (FIG. 1).
Reference may be made to commonly-owned U.S. Patent Publication No.
2004/0267156, filed Apr. 4, 2004, for a detailed discussion
regarding the components and functionality of deployment assembly
50, the entire contents of which is incorporated herein.
[0034] In one embodiment, as seen in FIG. 4, antenna assembly 100
includes a distal portion 102a of an inner conductor that exhibits
a substantially arcuate or curved profile when deployed. FIG. 4
shows the antenna assembly 100 in a partially deployed
configuration. Reference may be made to commonly-owned U.S. Pat.
No. 7,197,363 for a detailed discussion of the structure of arcuate
microwave antenna configurations, the entire contents of which is
incorporated herein.
[0035] With continued reference to FIGS. 3 and 4, the sheath 116 is
disposed about distal portion 102a of the inner conductor in such a
manner so as to define a lumen 128. Sheath 116 may be fixedly,
releasably, or slidably connected to distal portion 102a in any
suitable manner including, but not being limited to, welding or
adhering, as would be appreciated by one skilled in the art. Sheath
116 has proximal and distal ends 130, 132 defined by the points at
which sheath 116 is connected to distal portion 102a. In one
embodiment, as best seen in FIG. 4, the distal-most tip 134 of
distal portion 102a extends beyond the distal end 132 of sheath
116. In another embodiment, the sheath 116 may be connected to the
distal portion 102a of an inner conductor 102 at the distal-most
tip 132 thereof, or at a point therebeyond (not shown).
[0036] The proximal end 130 of sheath 116 may be located at any
suitable location along the length of distal portion 102a of the
inner conductor, dependent upon the desired volume of lumen 128.
Although depicted as substantially incisive, the present disclosure
contemplates that distal-most tip 134 may be substantially arcuate,
duckbilled, or any other such configuration suitable for
facilitating the entry of the microwave tissue treatment device
into the tissue of a patient.
[0037] Sheath 116 may be formed of any suitable biocompatible,
impermeable material capable of retaining gas and/or fluid therein,
including and not limited to PTFE and
tetrafluorethylene-perfluorpropylene (FEP). The present disclosure
contemplates that sheath 116 may be either substantially rigid, or
substantially non-rigid in character.
[0038] Referring back to FIG. 1, the fill source 40 operates in
conjunction with, and is fluidly connected to, lumen 128 of sheath
116 such that one or more dielectric materials (e.g., fluids or
gases) may be circulated therethrough. The dielectric compounds
also serve to dissipate some of the heat generated by the antenna
assembly during use in addition to acting as a medium that modifies
the dielectric constant of the distal portion of the antenna
assembly. Suitable dielectric fluids include, but are not limited
to, water, saline, liquid chlorodifluoromethane, or any suitable
perfluorocarbon fluid, such as Fluorinert.RTM., distributed
commercially by Minnesota Mining and Manufacturing Company
(3M.TM.), St. Paul, Minn., USA. Suitable dielectric gases include
air, nitrogen, nitrous oxide, carbon dioxide and the like. In yet
another variation, a combination of liquids and/or gases may be
utilized. The compounds circulated through the lumen 128 may vary
depending upon the desired cooling rate and the desired tissue
impedance matching properties. The fill source 40 includes a
suitable pump configured to supply the dielectric material "M" to
the lumen 128. If fluid is being used, the pump may be any type of
peristaltic pump and the like. If gas is being used, any type of
electric gas pump or compressor may be utilized.
[0039] FIG. 5 shows the antenna assembly 100 in a fully deployed
configuration, in which the inner conductor 102 fully encompasses a
tissue volume "T" targeted for ablation. The inner conductor 102 is
formed from a flexible metal suitable to curve about the tissue
volume "T" such that the produced ablation volume when the inner
conductor 102 is energized by the microwave energy encompasses the
tissue volume "T." The inner conductor 102 may be made from a shape
memory alloy, e.g., Nitinol or some other similar alloy, such that
as distal portion 102a is inserted within the tissue, the distal
portion 102a may form the curved and/or helical shape about the
tissue volume "T" within the formed ablation volume. The inner
conductor 102 extends laterally in relation to the longitudinal
axis "A" to define an ablation region that surrounds the tissue
volume "T" to be treated in such a manner that the tissue volume
"T" is located within the ablation region
[0040] In one embodiment, the inner conductor may be formed from a
0.022'' Nitinol wire and the sheath 116 may be formed from PTFE
sleeve having an inner diameter of about 0.022'' and an outer
diameter of about 0.050.'' The sheath 116 may be inflated using the
fill source 40 to adjust the dielectric properties along the length
of the inner conductor 102. The sheath 116 may be in a deflated
state during the deployment of inner conductor 102 within the
tissue. Once inner conductor 102 has been desirably positioned,
sheath 106 may be filled with the desired dielectric material "M,"
until the sheath 116 has inflated sufficiently about the inner
conductor 102. The size of inflated sheath 116 may be varied
according to the desired radiative effects, the length of deployed
inner conductor 102, as well as the type of tissue.
[0041] FIG. 6 shows the cross-sectional view of the antenna
assembly 100. The dielectric material "M" is supplied to the lumen
128 to provide a dielectric gap "G" between the inner conductor 102
and the sheath 116. The antenna assembly 100 may be curved, as
shown in FIG. 5, to position the gap "G" toward the center of
curved antenna assembly 100.
[0042] In one embodiment, the lumen 128 may be filled with any
dielectric material "M" having a relatively low dielectric
permittivity as compared to the material forming the sheath 116. In
another embodiment, the lumen 128 may be filled with air, since air
has a dielectric constant of 1. A lower dielectric permittivity
within the lumen 128 allows for microwave energy to travel through
the gap "G" easier than through the sheath 116. Therefore,
positioning of the inner conductor 102 in contact with the sheath
116 (e.g., off-center) and curving the antenna assembly 100 such
that the gap "G" is facing toward the center of the curved antenna
assembly 100 directs the microwave energy toward the center of the
looped antenna assembly 100. In particular, this configuration of
the gap "G" directs the microwave energy into the looped antenna
assembly 100 more efficiently along the inside thereof as opposed
to the outside. In other words, this configuration maximizes
matching toward the center of the curved inner conductor 102,
allowing for better microwave transmission, thereby maximizing
ablation within the inner conductor 102. Conversely, this
configuration minimizes effects outside the curved inner conductor
102, since the dielectric material "M" of the sheath 116 limits
microwave transmission and provides for poor impedance matching
between the tissue and the antenna assembly 100.
[0043] FIG. 7 shows another embodiment of an antenna assembly 200
having an inner conductor 202 disposed within a multi-lumen sheath
216. The antenna assembly 200 may be curved in a similar manner as
the antenna assembly 100 as shown in FIG. 5. The sheath 216
includes two or more lumens 228 and 229 defined therein. The
multi-lumen configuration allows for first lumen 228 to provide for
a dielectric gap "G" between the inner conductor 202 and the sheath
216 and the inner conductor 202 to be disposed within the second
lumen 229. Multi-lumen structure allows for molding of the first
lumen 228 to achieve a predetermined shape of the dielectric gap
"G" suitable for directing microwave energy into the center of the
curved inner conductor 202.
[0044] FIG. 8 shows a further embodiment of an antenna assembly 300
having an inner conductor 302 disposed within a sheath 316 having a
lumen 328 defined therein. The antenna assembly 300 may be curved
in a similar manner as the antenna assembly 100 as shown in FIG. 5.
The inner conductor 302 has a substantially hemi-spherical
cross-section. This geometry subdivides the lumen 328 to form a
dielectric gap "G" between the inner conductor 302 and the sheath
316.
[0045] FIG. 9 also shows another embodiment of an antenna assembly
400 having an inner conductor 402 of different geometries. The
antenna assembly 400 may be curved in a similar manner as the
antenna assembly 100 as shown in FIG. 5. The inner conductor 402
has a substantially U-shaped cross-section. This geometry also
subdivides the lumen 428 to form a dielectric gap "G" between the
inner conductor 402 and the sheath 416.
[0046] The cross-sectional shape of the inner conductors 302 and
402 provide for an enhanced dielectric gap "G." In particular, the
shape of the inner conductors 302 and 402 in combination with the
enhanced dielectric gaps "G" provide for directed deposition of
microwave energy toward the center of the curved antenna assemblies
300 and 400. In other words, these configurations direct the
microwave energy more efficiently along the inside thereof as
opposed to the outside.
[0047] FIGS. 10-12 show another embodiment of the antenna assembly
500. The antenna assembly 500 includes an elongated member 514
disposed about the distal portion 112 of feedline 30 (FIG. 1), and
a sheath 516 that at least partially surrounds a distal portion
502a of an inner conductor 502. The elongated member 514 is
substantially similar to the elongated member 114 and may also be
formed of any material suitable for electrically insulating a
clinician or operator from the inner conductor 502 disposed therein
such that the antenna assembly 500 may be handled during use. The
inner conductor 502 may be deployed from within the elongated
member 514 similar to the inner conductor 102 as discussed above
with respect to FIGS. 3-5.
[0048] FIG. 10 shows the antenna assembly 500 in a fully deployed
configuration, in which the inner conductor 502 fully encompasses a
tissue volume "T" targeted for ablation. The inner conductor 502 is
formed from a flexible metal suitable to curve about the tissue
volume "T" such that the produced ablation volume when the inner
conductor 502 is energized by the microwave energy encompasses the
tissue volume "T," The inner conductor 502 may be made from a shape
memory alloy, e.g., Nitinol or some other similar alloy, such that
as distal portion 502a is inserted within the tissue, it may be
preconfigured to form the curved shape as the inner conductor 502
is further inserted within the tissue.
[0049] The sheath 516 at least partially surrounds the distal
portion 502a of the inner conductor 502 and defines a lumen 528
thereabout. The sheath 516 may be fixedly, releasably, or slidably
connected to distal portion 502a in any suitable manner including,
but not being limited to, welding or adhering, as would be
appreciated by one skilled in the art. The sheath 516 may be formed
of any suitable biocompatible, impermeable material capable of
retaining gas and/or fluid therein, including, but not limited to,
PTFE and tetrafluorethylene-perfluorpropylene (FEP).
[0050] The sheath 516 is formed from a flexible expandable
material, such that during inflation, the sheath 516 expands to
accommodate the increased volume of the dielectric material "M."
The lumen 528 is in fluid communication with the fill source 40
such that one or more dielectric materials (e.g., fluids or gases)
may be circulated therethrough, which are used to inflate the
sheath 516.
[0051] Suitable dielectric fluids include, but are not limited to,
water, saline, liquid chlorodifluoromethane, or any suitable
perfluorocarbon fluid, such as Fluorinert.RTM., distributed
commercially by Minnesota Mining and Manufacturing Company
(3M.TM.), St. Paul, Minn., USA. Suitable dielectric gases include
air, nitrogen, nitrous oxide, carbon dioxide and the like. In yet
another variation, a combination of liquids and/or gases may be
utilized. The selection of dielectric mixtures may be used to
provide for better matching microwave energy to different tissue
types and sizes.
[0052] In addition to the varying dielectric properties of the
dielectric compounds, the flexible nature of the sheath 516 also
provides for dynamic impedance matching by varying the amount of
dielectric material "M" filling the lumen 528. The varying amount
of the dielectric material "M" affects the bulk impedance of the
antenna assembly 500 based on: (1) the amount of the dielectric
material "M" present and (2) the dimension of the sheath 516, which
is also based on the amount of the dielectric material "M" present
therein.
[0053] Based on the dielectric constant of the material, the amount
of the dielectric material "M" may be used to increase or decrease
the dielectric permittivity of the antenna assembly 500. More
specifically, if a dielectric material "M" having a dielectric
constant of 2 or more is used then increasing the amount of the
material within the lumen 528 reduces the effectiveness of
microwave transmission. If a dielectric material "M" having a
dielectric constant of 1 or less is used then increasing the amount
of such material within the lumen 528 increases the effectiveness
of microwave transmission.
[0054] The dielectric material "M" may also be used to vary
dielectric permittivity of the sheath 516. As shown in FIGS. 11 and
12, the thickness of the sheath 516 varies based on the pressure
within the lumen 528 (e.g., amount of the dielectric "M" present
therein). Under lower pressure, as illustrated in FIG. 11, the
sheath 516 has a relatively large thickness w.sub.1. The elasticity
of the sheath causes contraction, which increases the wall
thickness w.sub.1 resulting in a higher overall dielectric constant
of the sheath 516. Under higher pressure, as illustrated in FIG.
12, the sheath has a thinner thickness w.sub.2. Increasing the
pressure within the lumen 528 expands the sheath 516, thereby
decreasing the wall thickness w.sub.2 while reducing the overall
dielectric constant of the sheath 516.
[0055] FIGS. 13 and 14 illustrate another embodiment of the antenna
assembly 500 having the expandable sheath 516. In particular, the
antenna assembly 500 includes a dielectric permeable core 529
within the lumen 528. The core 529 may be formed from any suitable
fibrous or porous dielectric material which may be permeable to the
dielectric material "M" (e.g., sponge, fiberglass mesh, etc.). The
core 529 is secured to the inner conductor 502 and the inner
surface of the sheath 516, such that as the sheath 516 is deflated
and inflated, the core 529 expands and contracts accordingly, as
shown in FIGS. 13 and 14, respectively.
[0056] The core 529 provides structural integrity to the antenna
assembly 500 by securing the inner conductor 512 at the center of
the sheath 516. In addition, the dielectric material of the core
529 provides additional dielectric matching capabilities to the
antenna assembly 500. The porous and/or fibrous structure of the
core 529 allows the thickness of the sheath 516 to be varied as
discussed above with respect to FIGS. 11 and 12. In particular, the
thickness of the sheath 516 varies based on the pressure within the
lumen 528 (e.g., amount of the dielectric "M" present therein).
Under lower pressure, as illustrated in FIG. 13, the sheath 516 has
a relatively large thickness w.sub.1. The elasticity of the sheath
causes contraction, which increases the wall thickness w.sub.1
resulting in a higher overall dielectric constant of the sheath
516. In the deflated configuration, the core 529 in combination
with the thickened sheath 516 act as the primary dielectric
buffers. Thus, the core 529 may be formed from a dielectric
material that is suitable for impedance matching the antenna
assembly 500 in the deflated state.
[0057] Under higher pressure, as illustrated in FIG. 14, the sheath
has a thinner thickness w.sub.2. Increasing the pressure within the
lumen 528 expands the sheath 516, thereby decreasing the wall
thickness w.sub.2 while increasing the volume of the lumen 528.
This, in turn, reduces the overall dielectric constant of the
sheath 516.
[0058] FIG. 15 illustrates a flow chart of a method for varying the
dielectric properties of the antenna assembly 500. In step 600, the
antenna assembly 500 is inserted into tissue and is deployed to
surround the tissue volume "T" as shown in FIG. 10. In step 602,
the sheath 516 is inflated to a predetermined volume such the
sheath 516 is stretched to the thickness w.sub.2. The thinner
thickness w.sub.2 provides for a lower dielectric permittivity,
thereby providing for optimum impedance matching with undesiccated
tissue. In step 604, the antenna assembly 500 is energized to
ablate the tissue volume "T." As a result of the energy
application, the tissue volume "T" is desiccated and the impedance
thereof increases accordingly. In step 606, the sheath 516 is
deflated by withdrawing the dielectric material "M." As the sheath
516 is deflated, the pressure is decreased, increasing the
thickness w.sub.1 of the sheath 516, thereby increasing the
dielectric constant of the sheath 516 to provide for better
dielectric matching with desiccated tissue. During step 606,
microwave energy may be continuously supplied to the antenna
assembly 500. In step 608, additional microwave energy is supplied
to the antenna assembly 500. Steps 606 and 608 may be repeated
multiple times to provide for step-down adjustments of the
dielectric permittivity of the antenna assembly 500.
[0059] The described embodiments of the present disclosure are
intended to be illustrative rather than restrictive, and are not
intended to represent every embodiment of the present disclosure.
Various modifications and variations can be made without departing
from the spirit or scope of the disclosure as set forth in the
following claims both literally and in equivalents recognized in
law.
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